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Abstract:

Liquid cooled LED systems are disclosed. Embodiments of the invention
provide an LED lighting system in which the LED devices are cooled by
circulating liquid or fluid. In example embodiments, a flow return member
provides a way for a fluid medium to enter and exit an envelope
containing the LED devices. An additional cooling mechanism, such as a
radiator or thermoelectric cooler can be provided. The optically
transmissive fluid medium can be, for example, oil or a fluorinated or
halogenated liquid or gel, and can optionally provide index matching. The
fluid medium can optionally include a phase change material in order to
enhance cooling. In some embodiments, a pump is used to circulate the
fluid medium. However, the optical envelope and/or the flow return member
could also be oriented so that the fluid medium circulates by gravity
and/or temperature difference.

Claims:

1. A lighting system comprising: an optically transmissive envelope; an
array of LED devices within the optically transmissive envelope to be
operable to emit light when energized; an optically transmissive fluid
medium in thermal communication with the array of LED devices; and a flow
return member in fluid communication with the optically transmissive
envelope so that the optically transmissive fluid medium can circulate
through the optically transmissive envelope.

2. The lighting system of claim 1 further comprising a radiator.

3. The lighting system of claim 1 further comprising a thermoelectric
cooler in thermal communication with the optically transmissive fluid
medium.

4. The lighting system of claim 1 further comprising a pump in fluid
communication with at least one of the optically transmissive envelope
and the flow return member.

5. The lighting system of claim 1 wherein at least one of the optically
transmissive envelope and the flow return member is oriented so that the
fluid medium circulates by at least one of gravity and temperature
difference.

6. The lighting system of claim 1 wherein the optically transmissive
fluid medium comprises at least one of oil and a fluorinated or
halogenated liquid or gel.

7. The lighting system of claim 6 wherein the optically transmissive
fluid medium is an index matching medium.

8. The lighting system of claim 6 further comprising phosphor disposed
within or on the optically transmissive envelope.

9. The lighting system of claim 8 wherein the optically transmissive
envelope filters light to exhibit a spectral notch between 520 nm and 605
nm.

11. The lighting system of claim 6 wherein the array of LED devices
further comprises a plurality of LED devices connected in series.

12. The lighting system of claim 11 wherein the electrical connection is
configured to supply the array of LED devices with alternating current.

13. The lighting system of claim 11 wherein the electrical connection is
configured to supply the array of LED devices with direct current.

14. The lighting system of claim 1 wherein the array of LED devices
further comprises a plurality of LED devices connected in parallel.

15. The lighting system of claim 14 wherein the flow return member and
optically transmissive envelope are configured so that the optically
transmissive fluid medium circulates in a direction that opposes a
voltage drop through the plurality of LED devices.

16. The lighting system of claim 1 further comprising: an internal
envelope between the optically transmissive envelope and the array of LED
devices; and an internal coolant disposed in the internal envelope.

17. The lighting system of claim 16 wherein the internal coolant
comprises at least one of oil and a fluorinated or halogenated liquid or
gel.

19. A light fixture comprising: an optically transmissive tubular
envelope; a linear array of LED devices disposed in the tubular envelope
to be operable to emit light when energized; a reflector configured to
reflect light from the linear array of LED devices; an optically
transmissive fluid medium in thermal communication with the linear array
of LED devices; a flow return member in fluid communication with the
tubular envelope so that the optically transmissive fluid medium can
circulate through the tubular envelope; and a power supply connected to
the linear array of LED devices.

20. The light fixture of claim 19 wherein the flow return member is
configured to dissipate heat from the optically transmissive fluid
medium.

21. The light fixture of claim 19 further comprising a thermoelectric
cooler in thermal communication with the optically transmissive fluid
medium.

22. The light fixture of claim 19 wherein the optically transmissive
fluid medium comprises at least one of oil and a fluorinated or
halogenated liquid or gel.

24. The light fixture of claim 19 wherein the linear array of LED devices
further comprises a plurality of LED devices connected in series.

25. The light fixture of claim 19 wherein the linear array of LED devices
further comprises a plurality of LED devices connected in parallel.

26. The light fixture of claim 25 wherein the flow return member and
optically transmissive tubular envelope are configured so that the
optically transmissive fluid medium circulates in a direction that
opposes a direction of voltage drop through the plurality of LED devices.

27. A method of operating an LED lighting system, the method comprising:
energizing a linear LED array; circulating an optically transmissive
fluid through an optical envelope surrounding the linear LED array; and
dissipating heat from the optically transmissive fluid.

28. The method of claim 27 further comprising circulating the optically
transmissive fluid through a flow return member.

29. The method of claim 28 wherein the dissipating of the heat is
accomplished by radiating the heat.

30. The method of claim 28 wherein the dissipating of the heat is
accomplished by passing the optically transmissive fluid through a
thermoelectric cooler.

31. The method of claim 28 wherein the dissipating of the heat is
accomplished by causing a phase change in the optically transmissive
fluid.

32. The method of claim 28 further comprising energizing a phosphor.

33. The method of claim 32 further comprising filtering a visible light
intensity so that the intensity is comparatively reduced within a
predetermined part of a spectrum of visible light.

34. The method of claim 28 wherein at least one of the circulating of the
optically transmissive fluid through the optical envelope and the
circulating of the optically transmissive fluid through the flow return
member further comprises pumping the optically transmissive fluid.

35. The method of claim 28 wherein the circulating of the optically
transmissive fluid through the optical envelope further comprises
circulating the optically transmissive fluid in a direction that opposes
a voltage drop in the linear LED array.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of and claims priority
from commonly owned, co-pending application Ser. No. 13/340,928, filed
Dec. 30, 2011, the entire disclosure of which is incorporated herein by
reference.

BACKGROUND

[0002] Light emitting diode (LED) lighting systems are becoming more
prevalent as replacements for existing lighting systems. LED systems are
an example of solid state lighting (SSL) and have advantages over
traditional lighting solutions such as incandescent and fluorescent
lighting because they use less energy, are more durable, operate longer,
can be combined in multi-color arrays that can be controlled to deliver
virtually any color light, and generally contain no lead or mercury. A
solid state lighting system may take the form of a lighting unit, light
fixture, light bulb, or a "lamp."

[0003] An LED lighting system may include, for example, a packaged light
emitting device including one or more light emitting diodes (LEDs), which
may include inorganic LEDs, which may include semiconductor layers
forming p-n junctions and/or organic LEDs (OLEDs), which may include
organic light emission layers. Light perceived as white or near-white may
be generated by a combination of red, green, and blue ("RGB") LEDs.
Output color of such a device may be altered by separately adjusting
supply of current to the red, green, and blue LEDs. Another method for
generating white or near-white light is by using a lumiphor such as a
phosphor. Still another approach for producing white light is to
stimulate phosphors or dyes of multiple colors with an LED source. Many
other approaches can be taken.

[0004] LED units often include some type of optical element or elements to
allow for localized mixing of colors, collimate light, or provide a
particular light pattern. Sometimes the optical element also serves as an
envelope or enclosure for the electronics and/or the LEDs. A power supply
can be included in the system along with the LEDs or LED packages and the
optical components. The heat generated by the LEDs can raise the
temperature of the power supply components, and/or vice versa, and the
resulting temperature increase must be taken into account in the system
design. A heatsink, heat pipe and/or other heat removal or dissipation
elements are also often needed to cool the LEDs and/or power supply in
order to maintain appropriate operating temperature for the LEDs and any
other electronics in the system.

SUMMARY

[0005] Embodiments of the present invention provide an LED lighting system
in which the LED devices are cooled by circulating liquid or fluid. In
example embodiments, a flow return member provides a way for a fluid
medium to enter and exit an envelope containing the LED devices. In at
least some embodiments, an additional cooling mechanism, such as a
radiator or thermoelectric cooler can be provided. Embodiments of the
invention can use an LED array of various configurations and shapes,
although some embodiments can be most readily used with linear LED
lighting systems and fixtures. Such linear arrays might be used, for
example, in decorative lighting, or to replace the tubular bulbs
sometimes used in xenon directional lamps.

[0006] A lighting system according to some embodiments of the invention
includes an optically transmissive envelope and an array of LED devices
disposed in the optically transmissive envelope to be operable to emit
light when energized. The envelope can include an optically transmissive
fluid medium in thermal communication with the array of LED devices. A
flow return member is disposed to be in fluid communication with the
optically transmissive envelope so that the optically transmissive fluid
medium can circulate through the optically transmissive envelope. In some
embodiments, an additional internal envelope can be provided between the
optically transmissive envelope and the array of LED devices. This
internal envelope can contain an internal coolant, which can be of the
same or a different make up as the optically transmissive fluid and may
or may not be circulating.

[0007] In some embodiments, additional cooling for the lighting system can
be provided by a radiator such as a collection of cooling coils or some
other passive structure. In some embodiments, additional cooling can be
provided by a thermoelectric cooler such as a Peltier device in thermal
communication with the optically transmissive fluid medium. The optically
transmissive fluid medium can be, for example, oil or a fluorinated or
halogenated liquid or gel, and can optionally provide index matching. The
fluid medium can optionally include a phase change material in order to
enhance cooling. In some embodiments, a pump is used to circulate the
fluid medium. In some embodiments the envelope and/or the flow return
member is/are oriented so that the fluid medium circulates by gravity
and/or temperature difference.

[0008] In some embodiments of the invention, a phosphor or phosphors can
be used within or on the optical envelope to improve the color rendering
index of the light from the system. Such a phosphor, for example, can be
applied to an individual LED dies, can be applied to or dispersed in the
envelope material, or can be suspended in the fluid medium. The optical
envelope of the lighting system can also optionally act as a notch
filter. In some embodiments, a spectral notch can be produced by the
notch filter, where the notch occurs between 520 nm and 605 nm in the
visible spectrum of visible light.

[0009] In some embodiments of the invention, the array of LED devices may
include a plurality of LED devices connected in series. The devices can
be configured to use direct or alternating current. In some embodiments,
the array of LED devices includes a plurality of LED devices connected in
parallel. In either case, an LED device may be or include an individual
LED chip, or may be a multichip device either with or without a submount
or other carrier. The LED chips may be encapsulated or may be directly in
contact with the fluid medium. In embodiments where a parallel electrical
connection is used, the flow return member and optically transmissive
envelope of the lighting system can be configured so that the optically
transmissive fluid medium circulates in a direction that opposes a
voltage drop through the plurality of connected LED devices. Such a
configuration can enable the effects of the temperature increase in the
fluid as it absorbs heat from the LED devices to at least in part balance
out the effects of the voltage drop in a linear array of LED devices.

[0010] A lighting system according to example embodiments of the invention
may find use in any of various light fixtures with a power supply and a
reflector or other optical elements as appropriate. As an example, a
lighting system according to an embodiment of the invention with a
tubular optical envelop and/or a linear array of LED devices could be
used in a flood or spot self-contained light fixture such as the type
used in commercial architectural lighting or theatrical lighting. In such
a case, the linear light source of the lighting system of an embodiment
of the invention can replace the xenon tubular bulb that would otherwise
be used, while the reflector design and overall form factor of the
fixture could be maintained. Whether the lighting system is used in such
a fixture, or in some other application, in operation the LEDs are
energized and the optically transmissive fluid is passed through the
optical envelope surrounding the LED array. Provision can be made for
dissipating the heat from the optically transmissive fluid. Traditional
versions of the flood or spot fixtures mentioned sometimes include a
structure for dissipating heat, which could be used to house the radiator
or thermoelectric cooler previously mentioned.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIGS. 1-4 illustrate various examples of a lighting system
according to example embodiments of the present invention.

[0012] FIG. 5 illustrates a light fixture making use of a system according
to example embodiments of the invention.

[0013] FIGS. 6 and 7 provide magnified views of a linear array of LED
devices connected in series and disposed within an optical envelope
according to example embodiments of the invention.

[0014] FIG. 8 provides a magnified view of a linear array of LED devices
connected in parallel and disposed within an optical envelope according
to example embodiments of the invention.

[0015] FIG. 9 provides a magnified view of a portion of a lighting system
according to some embodiments of the invention, with an internal optical
envelope, which is in turn inside an optical envelope through which a
fluid medium is circulating.

DETAILED DESCRIPTION

[0016] Embodiments of the present invention now will be described more
fully hereinafter with reference to the accompanying drawings, in which
embodiments of the invention are shown. This invention may, however, be
embodied in many different forms and should not be construed as limited
to the embodiments set forth herein. Rather, these embodiments are
provided so that this disclosure will be thorough and complete, and will
fully convey the scope of the invention to those skilled in the art. Like
numbers refer to like elements throughout.

[0017] It will be understood that, although the terms first, second, etc.
may be used herein to describe various elements, these elements should
not be limited by these terms. These terms are only used to distinguish
one element from another. For example, a first element could be termed a
second element, and, similarly, a second element could be termed a first
element, without departing from the scope of the present invention. As
used herein, the term "and/or" includes any and all combinations of one
or more of the associated listed items.

[0018] It will be understood that when an element such as a layer, region
or substrate is referred to as being "on" or extending "onto" another
element, it can be directly on or extend directly onto the other element
or intervening elements may also be present. In contrast, when an element
is referred to as being "directly on" or extending "directly onto"
another element, there are no intervening elements present. It will also
be understood that when an element is referred to as being "connected" or
"coupled" to another element, it can be directly connected or coupled to
the other element or intervening elements may be present. In contrast,
when an element is referred to as being "directly connected" or "directly
coupled" to another element, there are no intervening elements present.

[0019] Relative terms such as "below" or "above" or "upper" or "lower" or
"horizontal" or "vertical" may be used herein to describe a relationship
of one element, layer or region to another element, layer or region as
illustrated in the figures. It will be understood that these terms are
intended to encompass different orientations of the device in addition to
the orientation depicted in the figures.

[0020] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of the
invention. As used herein, the singular forms "a", "an" and "the" are
intended to include the plural forms as well, unless the context clearly
indicates otherwise. It will be further understood that the terms
"comprises" "comprising," "includes" and/or "including" when used herein,
specify the presence of stated features, integers, steps, operations,
elements, and/or components, but do not preclude the presence or addition
of one or more other features, integers, steps, operations, elements,
components, and/or groups thereof.

[0021] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this invention
belongs. It will be further understood that terms used herein should be
interpreted as having a meaning that is consistent with their meaning in
the context of this specification and the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly so
defined herein. Unless otherwise expressly stated, comparative,
quantitative terms such as "less" and "greater", are intended to
encompass the concept of equality. As an example, "less" can mean not
only "less" in the strictest mathematical sense, but also, "less than or
equal to."

[0022] Embodiments of the present invention provide an LED lighting system
in which the LED devices are cooled by circulating, optically
transmissive fluid medium. In example embodiments, a flow return member
provides a way for a fluid medium to enter and exit an optically
transmissive envelope containing the LED devices. In at least some
embodiments, an additional cooling mechanism, such as a radiator or
thermoelectric cooler can be provided. Embodiments of the invention can
use an LED array of various configurations and shapes. Embodiments shown
with linear LED lighting systems and/or fixtures are presented as
examples only. Likewise, the optical envelope or enclosure can take
various shapes, for example spherical or a flat rectangular shape. The
optical envelope could also be designed with multiple entry and exit
points for the coolant being used. It should also be noted that although
the optically transmissive fluid can be said to be in thermal
communication with the LED devices, this thermal communication could be
either direct or indirect. In the indirect case, there could be other
intervening structures or even an additional fluid-filled envelope
through which heat passes.

[0023] In example embodiments of the invention, either or both of the
fluid medium used for cooling, and the optical envelope through which the
fluid medium circulates, may be described herein as optically
transmissive. The phrase "optically transmissive" means that a large
proportion of light passes through the material. The phrase does not
necessarily imply transparency, although a transparent material in either
case would certainly be considered optically transmissive. However,
either or both of the fluid medium and the envelope (as well as other
components) can be and should be considered optically transmissive if
they are diffusive as well. In fact, in some applications, it is
advantageous to provide a diffusive optical envelope and/or fluid for the
LED devices to provide color mixing. Furthermore, these components are
considered optically transmissive if they include a phosphor to provide
wavelength conversion or partial wavelength conversion, since even if the
emitted light has a different wavelength than the light incident on the
material, light is still being transmitted.

[0024] FIG. 1 illustrates a lighting system according to some example
embodiments of the invention. Lighting system 100 includes an optically
transmissive envelope 102 and a flow return member 104. The optical
envelope in this and other embodiments may be a flexible or rigid
transparent or diffusive light transmissive vinyl, polymer, or glass. The
flow return member in this example is made of metal. Reservoir 106 is
provided to hold excess cooling liquid. Pump 108 is provided to cause the
optically transmissive fluid to circulate through envelope 102 and flow
return member 104. The circulating optically transmissive fluid is in
thermal communication with the array of LED devices. Connector 110 in
fluid reservoir 106 provides a power interface, with leads supplying
power to pump 108 as well as an array of LED devices 116 shown
schematically within optically transmissive envelope 102. The reservoir
acts as a sealed terminal box that allows wiring to the system without
leakage. Further details of possible configurations of LED devices will
be discussed later in this disclosure, for example, with respect to FIGS.
6-8.

[0025] Still referring to FIG. 1, the flow return member also includes an
additional cooling mechanism, radiator 118, which is in this embodiment,
a series of metal coils through which the fluid medium passes. System 100
can include a power supply (not shown), which can be installed in the
fluid reservoir or in pipe 120, which supplies the liquid to optical
envelope 102. A small and efficient power supply could also be installed
in the optical envelope. In many embodiments, the power supply can be
cooled by the same circulating fluid medium that cools the LED devices.
Alternatively, the system can operate from alternating current, or direct
current supplied by an external source.

[0026]FIG. 2 illustrates a lighting system according to additional
embodiments of the invention. Lighting system 200 includes optically
transmissive envelope 202 and a flow return member 204. Reservoir 206 is
again provided to hold excess optically transmissive fluid. Pump 208
circulates the fluid through envelope 202 and flow return member 204.
Connector 210 in the fluid reservoir provides a power connection for the
pump and the light source an array of LED devices 216. In the example of
FIG. 2, the additional cooling mechanism 218 for the system can be any
powered device or collection of devices, such as a fan and coil
arrangement, a traditional HVAC-style cooling system, or a thermoelectric
cooler such as a Peltier device installed between the flow return member
and the pump. Pipe 220 connects the fluid reservoir to optical envelope
202. In this example, cooling mechanism 218 is connected to a power
source through its own cable 222; however, power could alternatively be
supplied through a passage to the reservoir 206 and connector 210. As
before, the system can include a power supply, can be powered by line
voltage, or be connected to a separate power supply. It should also be
noted that where the cooling mechanism is an HVAC-style system, the
refrigerant can be used as the optically transmissive fluid medium for
the system.

[0027]FIG. 3 illustrates a lighting system according to further
embodiments of the invention. Lighting system 300 includes optically
transmissive envelope 302 and a flow return member 304. In this
embodiment, reservoir 306 is provided to accumulate optically
transmissive fluid. However, in system 300, the optically transmissive
fluid is or includes phase change material so that the system acts like a
large heat pipe. The phase change provides additional cooling and drives
the fluid to circulate through optical envelope 302 and the flow return
member 304. Connector 310 provides a power connection for the LED devices
316 and in some embodiments includes a power supply or driver. Phase
change occurs in condenser 318, where the fluid condenses into liquid,
before dropping to reservoir 306 and circulating through the optical
envelope, where it vaporizes or partially vaporizes from heat generated
by the LED array. In example embodiments, the phase changes occur at the
hottest point in the system and in the condenser regardless of the
orientation of the lamp, thus the phase change material will provide
cooling regardless of how the system is positioned.

[0028]FIG. 4 illustrates a lighting system according additional
embodiments of the invention. The system of FIG. 4 is similar to the
system of FIG. 1 in most respects, except that there is no pump. In
system 400 of FIG. 4, gravity, temperature difference and the closed
nature of the system cause the optically transmissive fluid to circulate
when the system is operated in the vertical position, as indicated in the
drawing legend. Lighting system 400 includes optically transmissive
envelope 402 and metal flow return member 404. Connector 410 provides a
power connection for the LED devices 416 and in some embodiments includes
a power supply or driver. In the example of FIG. 4, the flow return
member again includes an additional cooling mechanism, radiator 418,
which is again in this embodiment, a series of metal coils through which
the fluid medium passes.

[0029] In some embodiments of the invention, it may be desirable to
confine any power supply to a relatively small space, inside the fluid
reservoir or a connecting tube for example. Various methods and
techniques can be used to increase the capacity and decrease the size of
a power supply, also sometimes called a "driver," in order to allow the
power supply for an LED lamp to be manufactured more cost-effectively, or
to take up less space. For example, multiple LED devices used in series
can be configured to be powered with a relatively high voltage.
Additionally, energy storage methods can be used in the driver design.
For example, current from a current source can be coupled in series with
LEDs, a current control circuit and a capacitor to provide energy
storage. A voltage control circuit can also be used. A current source
circuit can be used together with a current limiter circuit configured to
limit a current through the LEDs to less than the current produced by the
current source circuit. In the latter case, the power supply can also
include a rectifier circuit having an input coupled to an input of the
current source circuit.

[0030] Some embodiments of the invention can include a multiple LED sets
coupled in series. One set of LEDs, for example, may be included on each
of several submount-based devices that make up the LED array used in the
liquid-cooled system. The power supply in such an embodiment can include
a plurality of current diversion circuits, respective ones of which are
coupled to respective nodes of the LED sets and configured to operate
responsive to bias state transitions of respective ones of the LED sets.
Such circuits can be installed with sets of LEDs on submounts or be wired
between devices in a linear array. In some embodiments, a first one of
the current diversion circuits is configured to conduct current via a
first one of the LED sets and is configured to be turned off responsive
to current through a second one of the LED sets. The first one of the
current diversion circuits may be configured to conduct current
responsive to a forward biasing of the first one of the LED sets and the
second one of the current diversion circuit may be configured to conduct
current responsive to a forward biasing of the second one of the LED
sets.

[0031] In some of the embodiments described immediately above, the first
one of the current diversion circuits is configured to turn off in
response to a voltage at a node. For example a resistor may be coupled in
series with the sets and the first one of the current diversion circuits
may be configured to turn off in response to a voltage at a terminal of
the resistor. In some embodiments, for example, the first one of the
current diversion circuits may include a bipolar transistor providing a
controllable current path between a node and a terminal of a power
supply, and current through the resistor may vary an emitter bias of the
bipolar transistor. In some such embodiments, each of the current
diversion circuits may include a transistor providing a controllable
current path between a node of the sets and a terminal of a power supply
and a turn-off circuit coupled to a node and to a control terminal of the
transistor and configured to control the current path responsive to a
control input. A current through one of the LED sets may provide the
control input. The transistor may include a bipolar transistor and the
turn-off circuit may be configured to vary a base current of the bipolar
transistor responsive to the control input.

[0032] With any of the examples discussed, the system operates by
energizing an LED array, possibly using a power supply like that
described above, and circulating the optically transmissive fluid through
an envelope surrounding the LED array and possibly also surrounding the
power supply circuitry. In some embodiments, phosphor is energized along
with the appropriate LED chips. A flow return member is used to move the
fluid out of one end of the optical envelope of the system and into the
other end. It should be noted however that the optical envelop could take
various shapes. Thus the terms "one end" and "the other end" are used
only in reference to the entry points and exit points of fluid, which
serves as a coolant. As previously mentioned, additional mechanisms to
dissipate heat from the fluid as it circulates can be employed. Such an
additional mechanism can be used to radiate the heat from the fluid. A
thermoelectric cooler can be used to cool the fluid. Phase change of the
fluid material can be used. Two or more of these mechanisms can be
combined.

[0033] With respect to the fluid medium used with an embodiment of the
invention, as an example, a liquid, gas, gel, or other material that is
either moderate to highly thermally conductive, moderate to highly
convective, or both, can be used. As previously mentioned, the fluid
medium can be a refrigerant such as any of those used in residential or
commercial HVAC and refrigeration systems. Any or all of these can
generically be referred to as either a fluid or a liquid. As used herein,
a "gel" includes a medium having a solid structure and a liquid
permeating the solid structure. A gel can include a liquid, which is a
fluid. The term "fluid medium" is used herein to refer to gels, liquids,
and any other formable material. The fluid medium surrounds the LED
devices in the optical enclosure. In example embodiments, the fluid
medium is nonconductive enough so that no packaging or insulation is
needed for the LED devices, although packaging may be included. In
example embodiments, the fluid medium has low to moderate thermal
expansion, or a thermal expansion that substantially matches that of one
or more of the other components of the system. The fluid medium in at
least some embodiments is also inert and does not readily decompose. A
fluid medium can be any continuous, amorphous substance whose molecules
move freely past one another and that has the tendency to assume the
shape of its container. In addition to a liquid, a fluid medium can be a
gas such as helium.

[0034] As examples, the fluid medium used in some embodiments of the
invention can be oil. The oil can be petroleum-based, such as mineral
oil, or can be organic in nature, such as vegetable oil. The fluid medium
in some embodiments may also be a perfluorinated polyether (PFPE) liquid,
or other fluorinated or halogenated liquid, or gel. An appropriate
propylene carbonate liquid or gel having at least some of the
above-discussed properties might also be used. Suitable PFPE-based
liquids are commercially available, for example, from Solvay Solexis
S.p.A of Italy. In embodiments where a phase change material is used for
the fluid medium chloromethane, alcohol, methylene chloride or
trichloromonofluoromethane can be used. Flourinert® manufactured by
the 3M Company in St. Paul, Minn., U.S.A. can be used as coolant and/or a
phase change material. It should also be noted that water could be used
as a phase change material, since pressure inside the relevant portion of
lamp can be reduced in order to reduce the phase change temperature for
water.

[0035] In at least some embodiments, the optically transmissive fluid
medium is an index matching medium that is characterized by a refractive
index that provides for efficient light transfer with minimal reflection
and refraction from the LEDs through the enclosure. The index matching
medium can have the same or a similar refractive index as the material of
the optical envelope, the LED device package material or the LED
substrate material. The index matching medium can have a refractive index
that is arithmetically in between the indices of two of these materials.

[0036] As an example, if unpackaged LED chips are used for the LED devices
of the LED array, a fluid with a refractive index between that of the LED
substrates and the enclosure and/or inner envelope can be used. LEDs with
a transparent substrate can be used so that light passes through the
substrate and can be radiated from the light emitting layers of the chips
in all directions, assuming the LED chips are on a lead frame structure
without submounts. If the substrate chosen is silicon carbide, the
refractive index of the substrates is approximately 2.6. If glass is used
for the enclosure or envelope, the glass would typically have a
refractive index of approximately 1.5. Thus a fluid with a refractive
index of approximately 2.0-2.1 could be used as the index matching fluid
medium. LEDs with a sapphire substrate can also be used. Since the
substrate in this case would be an insulator, an ohmic contact would need
to pass through the substrate of the LED if an un-packaged die is used.
However, the refractive index of sapphire is approximately 1.7, so that
in this case if glass is again used for the enclosure or envelope, the
fluid medium could have a refractive index of approximately 1.6. If glass
lenses are used on packaged LED devices, the fluid could have an index of
approximately 1.5, essentially matching that of both the lenses and the
optical envelope.

[0037] LEDs and/or LED packages used with an embodiment of the invention
and can include light emitting diode chips that emit hues of light that,
when mixed, are perceived in combination as white light. Phosphors can be
used as described to add yet other colors of light by wavelength
conversion. For example, blue or violet LEDs can be used in the LED
assembly of the lamp and the appropriate phosphor can be in any of the
ways mentioned above. LED devices can be used with phosphorized coatings
packaged locally with the LEDs or with a phosphor coating the LED die.
For example, blue-shifted yellow (BSY) LED devices, which typically
include a local phosphor, can be used with a red phosphor on or in the
optically transmissive envelope to create substantially white light, or
combined with red emitting LED devices in the array to create
substantially white light. Such embodiments can produce light with a CRI
of at least 70, at least 80, at least 90, or at least 95. By use of the
term substantially white light, one could be referring to a chromacity
diagram including a blackbody locus of points, where the point for the
source falls within four, six or ten MacAdam ellipses of any point in the
blackbody locus of points.

[0038] A lighting system using the combination of BSY and red LED devices
referred to above to make substantially white light can be referred to as
a BSY plus red or "BSY+R" system. In such a system, the LED devices used
include LEDs operable to emit light of two different colors. In one
example embodiment, the LED devices include a group of LEDs, wherein each
LED, if and when illuminated, emits light having dominant wavelength from
440 to 480 nm. The LED devices include another group of LEDs, wherein
each LED, if and when illuminated, emits light having a dominant
wavelength from 605 to 630 nm. A phosphor can be used that, when excited,
emits light having a dominant wavelength from 560 to 580 nm, so as to
form a blue-shifted-yellow light with light from the former LED devices.
In another example embodiment, one group of LEDs emits light having a
dominant wavelength of from 435 to 490 nm and the other group emits light
having a dominant wavelength of from 600 to 640 nm. The phosphor, when
excited, emits light having a dominant wavelength of from 540 to 585 nm.

[0039] As another example, blue or violet LEDs can be used in a lighting
system and the appropriate phosphor can be included in any of the ways
mentioned. LED devices can be used with phosphorized coatings packaged
locally with the LEDs or with a phosphor coating the LED die. A lighting
system that produces warm white or cool white light can make use of two
phosphors, for example, calcium silicon nitride (CAS) red phosphor and/or
yttrium aluminum garnet (YAG) yellow phosphor. These phosphors can be
excited by blue LEDs by including one and/or both phosphors in LED
packages, on the LED die, in the fluid as well as in or on the optical
envelope of the system.

[0040] In some embodiments, if LED components that produce warm white
light are used for the LED array, the optical envelope of s system
according to embodiments of the invention can be made to notch filter the
light from the LED array to improve the color rendering capability of the
system. As an example, a rare earth compound such as neodymium oxide can
be used in or on the optical envelope. Due to the neodymium oxide or
other rare earth element in or on the optical envelope, light passing
through this optical element is filtered so that the light exiting the
optical envelope exhibits a spectral notch. In some embodiments, the rare
earth compound can be any or a combination of neodymium oxide, didymium,
dysprosium, erbium, holmium, praseodymium and thulium. A spectral notch
is a portion of the color spectrum where the light is attenuated, thus
forming a "notch" when light intensity is plotted against wavelength.
Depending on the type or composition of glass or other material used to
form the optical envelope, the amount of rare earth compound present, and
the amount and type of other trace substances in the optical element, the
spectral notch can occur between the wavelengths of 520 nm and 605 nm. In
some embodiments, the spectral notch can occur between the wavelengths of
565 nm and 600 nm. In other embodiments, the spectral notch can occur
between the wavelengths of 570 nm and 595 nm. Warm white light created by
a combination of LEDs and/or phosphor may be either oversaturated with
certain colors. In such systems, notch filtering can be used to alleviate
oversaturation, thereby improving the CRI of the system.

[0041] FIG. 5 illustrates a light fixture 500 according to an example
embodiment of the invention. Light fixture 500 makes use of a linear LED
array and optical envelope to create a spot light of the type that might
find use in theatrical applications. The linear LED light source can
serve as a replacement for the typical tubular xenon bulb used in such
applications. Linear optical envelope 502 and a metal flow return member
504 circulate optically transmissive liquid coolant. Reservoir 508
includes a pump (not shown) provided to cause optically transmissive
liquid to circulate through envelope 502 and flow return member 504. The
flow return member includes a series of metal coils through which the
fluid medium passes. An array of LED devices 516 is shown schematically
within optically transmissive envelope 502. Since the light source for
fixture 500 needs to be omnidirectional about the central axis of the
tubular optical envelope, bare, transparent LED dies are used on a wire
frame structure. Some dies are coated with a phosphor and the optical
envelope is frosted or otherwise textured to be diffusive and provide
appropriate color mixing.

[0042] Still referring to FIG. 5, fixture 500 includes a sheet steel
enclosure with three portions. Enclosure portion 530 includes the power
supply for the system as well as control circuitry (not shown). Enclosure
portion 532 includes various optical elements (not visible). For example,
enclosure portion 532 includes a reflector to direct the light out the
front of the fixture and produce a narrow beam of light. Typically, other
optical elements are present in portion 532 to allow the beam of light
produced to be soft or hard edges, to insert color filters into the light
path, and to adjust the beam angle and relative size of the spot formed
by the beam. Enclosure portion 534 provides a cosmetic shield for the
radiator for the liquid cooled LED lighting system and includes slots or
holes to allow heat to escape. Fixture 500 may optionally include a fan
to aid in cooling. Fixture 500 is powered by line cord 540 and supported
by an alt-azimuth stand, 542.

[0043] FIG. 6 shows a top perspective view of a portion of a tubular
optical envelope 600 with a plurality of LED devices 601 included inside.
The optical envelope is full of circulating liquid as previously
described. Three LED devices are shown in this part of the optical
envelope. In this particular example, all of the LEDs face the same
direction, though as mentioned elsewhere a system can be designed in
which the LEDs face different directions. The LED devices receive power
through metal strips 602 and 604, wherein strip 602 is a return lead, to
which the devices do not connect but are mechanically secured, and strip
604 provides for a series connection of the devices.

[0044] Still referring to FIG. 6, LED devices 601 in this example
embodiment makes use of submounts 702 and each include four
interconnected LED chips on metal layer portion 704 of the submount. The
anodes of the LED chips are on the bottom of the chips in this view and
are in contact with metal layer portion 704, which is in turn connected
to the positive terminal of the device. The cathodes of the LED chips are
connected by wire bonds to metal layer portion 706, which is in turn
connected to the negative terminal of the device. This arrangement allows
the plurality of LED chips to be placed close together and be relatively
small but still have relatively high efficiency and output. LED devices
601 could optionally include a lens, however in this embodiment they are
simply surrounded by the liquid within optical envelope 600.

[0045] Continuing with FIG. 6, the LED chips of devices 601 may be
selected from various light color bins to provide a combined light output
with a high color rendering index (CRI). The desired color mixing may be
achieved, for example, using blue, green, amber, red and/or red-orange
LED chips. In the Example of FIG. 6, LED chips 720 are coated or painted
with a phosphor and LED chips 724 are not. The optical envelope 600
includes color mixing treatment (not shown for clarity) by way of
texturing or frosting to cause the optical envelope to be diffusively
light transmissive.

[0046]FIG. 7 presents a bottom view of the LED light source and optical
element portion illustrated in FIG. 6. The positive and negative supply
terminals of devices 601 are indicated on the drawing. Strip 602 serves
as a supply return lead and makes no connection to devices 601, but
provides mechanical stability. The devices can be fastened to this lead
by adhesive, or in any other way. Lead 604 supplies power and
interconnects devices 601 in series, as can be appreciated by observing
the connection dots on each device, the middle dot being included
primarily to provide mechanical stability. These dots represent soldering
or weld points used to mechanically and/or electrically interconnect the
devices in series via strip 604. When connected in series as in FIGS. 6
and 7, the LED devices can be powered by a fairly high voltage and can be
AC powered since the LED devices also serve as rectifiers.

[0047] FIG. 8 shows a bottom view of a portion of a tubular optical
envelope 800 with a plurality of LED devices 801 included inside
according to another embodiment of the present invention. The optical
envelope is full of circulating liquid as previously described. Three LED
devices are shown in this part of the optical envelope. In this
particular example again, all of the LEDs face the same direction, though
as mentioned elsewhere a system can be designed in which the LEDs face
different directions. The LED devices receive power through metal strips
802 and 804, wherein strip 802 is connected to the positive terminal of
the power supply and all LED devices, and strip 804 serves as the
negative terminal. Thus, LED devices 801 in this embodiment are connected
in parallel. In practice, LED devices 801 can be similar or identical to
LED devices 601 pictured in FIGS. 6 and 7, but merely rotated ninety
degrees relative to the metal strips and optical envelope of the system.

[0048] Still referring to FIG. 8, additional options for a system
according to embodiments of the invention are illustrated. Firstly, as
can be seen in the drawing, the thickness of the optical envelope of the
system is shown exaggerated and includes fill dots to illustrate that the
material can be impregnated with phosphor, or a rare-earth compound to
provide notch-filtering, as previously discussed. Secondly, in the view
of FIG. 8, voltage can be supplied from the right, and the flow of
coolant can be from the left, in opposite directions. With such an
arrangement, the optically transmissive fluid medium circulates in a
direction that opposes a voltage drop through the plurality of LED
devices. The voltage drop is caused by the devices further and further
away from the power source being connected to the power source by longer
and longer lengths and by current drain through the preceding LED
devices. In a fixture with a tubular light source, this arrangement
causes the LED devices that are running at lower voltages to also be the
coolest. These two effects can cancel each other out, since lower
voltages typically mean lower currents, which reduce output, while cooler
temperatures for LEDs tend to increase output. It should be noted that in
any embodiment, as an alternative or in addition to the optically
transmissive envelope being impregnated with phosphor as discussed above,
phosphor particles can be suspended in the fluid medium. An embodiment
could be developed in which phosphor particles are suspended in the fluid
medium, and a rare-earth compound is used to impart notch-filtering
properties to the optical envelope material.

[0049] The effect of the temperature change over the length of a linear
fixture as coolant heats, especially if the coolant is circulating
relatively slowly can be minimized or eliminated if one has no desire to
use the effect to counteract voltage drop. One way to minimize this
temperature gradient is by using a reversible pump to circulate the fluid
medium, and causing the pump to reverse the fluid circulation direction
at regular intervals, or based on temperature sensing. Electronic
circuitry to accomplish this task can be included with the driver or
other control circuitry in the system, and can also be liquid cooled if
desired.

[0050] FIG. 9 shows a top perspective view of a portion of a lighting
system, a tubular optical envelope 900 with a plurality of LED devices
901 included inside. The optical envelope is full of circulating liquid
as previously described and as indicated by the arrows in the diagram.
Three LED devices are shown in this part of the optical envelope. In this
particular example, all of the LEDs face the same direction, though as
mentioned elsewhere a system can be designed in which the LEDs face
different directions. The LED devices and the way in which they are
supplied with power are similar to what has been previously described so
further details will not be discussed relative to FIG. 9.

[0051] Still referring to FIG. 9, LED devices 901 are further enclosed in
an internal envelope 960. The internal envelope can have any or all of
the optical properties and use any material previous described. It may
include a phosphor, filtering, and/or be diffusive to provide color
mixing. In the example embodiment of FIG. 9, internal envelop 960
contains an optically transmissive, insulative fluid medium, which is in
direct contact with the LED chips on LED devices 901. In this example
embodiment, the fluid in the internal envelope is stationary, but could
be made to circulate. A circulating fluid medium is contained in the
space between optical envelope 900 and internal envelope 960. Since this
fluid is only in contact with optical elements and not the LED devices,
it can be conductive and does not need to be inert. In this example
embodiment, water is used.

[0052] In some embodiments, the LED devices can face different directions,
or there can be multiple rows or strings of LED devices to render the
linear light source more omnidirectional relative to its axis. These
strings of LEDs can be created from individual, possibly transparent
chips on a wire structure or lead frame to create a light source that is
substantially omnidirectional about a linear axis. With the example given
above using multichip, submount-based LED devices, substantial
omnidirectional light can be obtained by simply turning some of the
devices around to face the opposite direction. Multiple strings of such
devices facing different directions can also be included, assuming a
large-enough optical envelope.

[0053] The various parts of a lighting system of fixture according to
example embodiments of the invention can be made of any of various
materials. A system or fixture according to embodiments of the invention
can be assembled using varied fastening methods and mechanisms for
interconnecting the various parts. In some embodiments, combinations of
fasteners such as tabs, latches or other suitable fastening arrangements
and combinations of fasteners can be used which would not require
adhesives or screws. In other embodiments, adhesives, solder joints,
welds, screws, bolts, or other fasteners and/or fastening techniques may
be used to fasten together the various components.

[0054] Although specific embodiments have been illustrated and described
herein, those of ordinary skill in the art appreciate that any
arrangement which is calculated to achieve the same purpose may be
substituted for the specific embodiments shown and that the invention has
other applications in other environments. This application is intended to
cover any adaptations or variations of the present invention. The
following claims are in no way intended to limit the scope of the
invention to the specific embodiments described herein.

Patent applications by Praneet Athalye, Morrisville, NC US

Patent applications by CREE, INC.

Patent applications in class LIGHT SOURCE OR LIGHT SOURCE SUPPORT AND LUMINESCENT MATERIAL

Patent applications in all subclasses LIGHT SOURCE OR LIGHT SOURCE SUPPORT AND LUMINESCENT MATERIAL